An Infrared Spectroscopic Investigation of Nitric Oxide Binding on Isolated Cobalt Cluster Cations

Nitric oxide binding to and/or dissociation on isolated cobalt cluster cations, Co_n⁺ (n = 3-14), has been investigated using a combination of infrared multiple photon dissociation spectroscopy and density functional theory. Rich vibrational structure in the 300-800 cm^-1 spectral region reflects predominantly dissociative adsorption, though a minor molecularly bound isomer cannot be ruled out. Inert messenger tagging reveals nitrogen and oxygen atoms bound in bridged and/or three-atom sites. The calculated potential energy surface associated with the reaction between NO and Co₃⁺ confirms only submerged barriers to dissociation and unusual full insertion of the N atom, which binds to all three metal atoms. The second NO adsorbed also dissociates on all clusters studied here, with the smallest cluster, [Co₃N₂O₂]⁺-Ar_m, adopting an unusual planar cyclic structure with O atoms and an N₂ molecule inserted between adjacent Co atoms.